Hellions soar through the skies atop bat-like skyboards. In game terms these are treated as jump packs, allowing the user to move 12" in the move phase whilst ignoring difficult or impassable terrain. A model riding a skyboard benefits from +1 to its Armour save.
Errata — Chapter Approved: Codex: Dark Eldar Q&A (v2.0): By the letter of the rules, a non-independent-character model could take a skyboard or Reaver jetbike, but unit coherency restrictions would reduce the benefit to little more than a Toughness/Armour boost, since the model couldn't meaningfully outrun the rest of its squad.